Caution: That's a boost converter, although it might work, you really want a regulator to drop the voltage from the transformer.
You would have to keep the transformer, rectifiers and reservoir capacitor so you have a DC voltage ahead of the regulator but typically it would be around 18V, dropping to about 14V under full load. The original regulator turned excess voltage and current into heat, you can do it more efficiently with a switch mode device like the ebay one but I would look for one more like this:
**broken link removed**
I have an application that uses six of them, all mounted side by side on heat conductive pads with a large heat sink behind them. If you keep them cool they can provide their 'peak' current all day long. My application is providing 12V to four security cameras and one control box. The other module is for charging a 12V car battery which gets switched in if there is an AC failure.
Brian.